Killshooter needs to be there simply because it creates more realistic combats than without it.
No, I'm not saying that without it your team mates would just kill you. I'm looking at it from the perspective that friendlies could just blaze away from behind you to get the enemy in front of you. The shots that hit you simply stop.
That bears no rememblence to WWII aircombat. In reality you didn't shoot in that situation because you might kill your squadronmate / friend / countrymen. In a game that line of reasoning doesn't work (unfortunately), so the only way to get
all players to check their fire when a friendly is in front of them is killshooter.
Now killshooter isn't perfect and accidents due to lag, or callous teammates, will happen. They aren't that common though.
I killshootered myself last week while flying a P-47D-11. A friendly had an FM2 on him so I rolled in behind the FM2 and started laying into it. I was getting hits when
I was back in the tower. The FM2 got credit for me. A single one of my bullets had hit the guy I was helping and the damage was allocated to my cockpit.
Oops.
Oh well, it happens sometimes and I'm more than willing to accept that kind of occasional irritation so that we can have combat that more closely resembles WWII aircrambat.